Meet The Candiru – The Penis Probing Fish Of Your Nightmares
Rather than go for an outward attack, the candiru implants itself inside the human body through a rather unusual entryway – the human penis.
The fish swims up the penis into the urethra – upstream, which is an impressive feat for such a small fish – where it latches onto the walls with barbs. Removal can be very difficult, as the barbs face one direction only, and pulling on the fish only causes them to sink deeper into the walls of the urethra.
https://allthatsinteresting.com/candiru